1. Field of the Invention
This invention relates to an automatic heating and cooling tank system for heating and cooling food.
2. Description of the Previously Published Art
Food products have been sterilized by heating them with steam in hermetically sealed containers. The high temperatures of the sterilization kill bacteria, but these same high temperatures also have an adverse effect on the food quality. The food, in effect, becomes "overcooked". Examples of these sterilization devices are disclosed in several U.S. Patents.
U.S. Pat. No. 3,215,538 relates to the sterilization of food products packaged in hermetically sealed containers. Fluid heat radiant means are used in an autoclave to balance the pressure increase within the containers.
U.S. Pat. No. 4,088,444 relates to the application of a fluid medium to food containers in a tank. A closed loop recirculating fluid system is used. The containers are prevented from becoming immersed within the bath formed in the tank.
U.S. Pat. No. 4,164,590. A plurality of spaced food containers are submitted to heat exchange by means of introduction of the spaced containers into a tank adapted with inlet and outlet means for a heat exchange fluid passing through said tank. The tank is maintained at higher than ambient pressure. The containers may be pouches (col. 3, line 62).
U.S. Pat. No. 4,784,053 relates to a food product cooker having compartments through which steam is introduced and withdrawn. A constant and uniform heating temperature is maintained.
U.S. Pat. No. 4,830,278 relates to an apparatus for steam sterilization of edible material containing pouches. In column 1 provision is made to apply a uniform temperature distribution. A predetermined pressure is maintained at all times.
Food products have also been cooked in a container where hot and cold water are supplied from storage tanks.
U.S. Pat. No. 4,505,192 relates to a cooker in which a number of cooking tanks are connected to central hot and cold water storage tanks and a piping and control system is provided such that the hot or cold water is repetitively fed and drained from the cooking tanks during the cooking process in a cyclic fashion. When hams are cooked in moulds they are contacted with heat carrying fluid for a relatively short period of time, then the fluid is removed for a relatively long period of time. This cycle is reproduced a certain number of times until the desired temperature is attained at the heart of the product.
U.S. Pat. No. 5,005,471 relates to a water bath cooker in which central hot and cold water storage tanks are disposed above a plurality of cooking tanks and are connected to the cooking tanks by a complex system of headers, pipes and valves.
Other devices for heating food include heated air as disclosed in U.S. Pat. No. 4,381,443 where packages containing precooked food are reheated in a rack over which heated air is passed.
In U.S. Pat. No. 4,752,490 food, such as hams, is conveyed through a heating unit where heated water in a basin is raised up to immerse the hams and cook them for a period of time. Then the hams move through a series of heating zones with each maintained at different temperatures where they are further heated in warm air.
In World Patent Publication 90/04928 a heating device moves the food along a conveyer and heated water is sprayed on one side.
3. Context of the Invention
The present invention relates to a process and an apparatus for the batch cooking of packaged foods to pasteurization temperatures, followed by rapid cooling to 38.degree. F. min., thus providing refrigerated products with an extended shelf life suitable for shipment, rethermalization, and consumption.
The overall process is known as sous vide--French for "under vacuum" meaning the products are packaged prior to cooking using a Form-Fill-Seal (FFS) machine. This machine utilizes roll stock to produce pouches of a seven layer structure with ethylene vinyl alcohol (EVOH) making up the barrier layer. Pouch package sizes range from about 2 oz. to 10 lbs. net weight. After forming, the pouch is filled with product and advances to the next sequence where it is vacuumized, heat sealed, and each individual pouch is cut-out and trimmed to size. Vacuumizing eliminates oxygen, which has a detrimetal effect on food product quality and reduces a product's shelf life.
Organoleptic considerations and sensory perceptions of taste, texture, aroma, and mouthfeel all require the products to be pasteurized, but not overcooked. Thus temperature sensing, control, and recording are critical in the process. Both the cooking temperature and time will vary depending on the product(s) as diverse as a 6 oz. chicken breast to an 8 lb. pouch of beef stroganoff. Thus there is a correlation in the environmental (process) water temperature with respect to the final internal (core) food temperature and the total heating/cooling curve.
It is of paramount importance to maintain a complete and unbroken record, through the thermal process, of both time and temperature. This begins with the ambient temperature of the food product, through the pasteurizing cooking cycle, and finally through the quick cooling cycle. After the food has been cooked it is necessary to prevent and reduce any chance of bacteria propagation by quickly reducing the temperature of the cooked food product to at least 38.degree. F. and preferably lower. This quick cooling is done prior to removal of the product from the cook/cool tank and into the final refrigerated storage. The cooling sequence is an integral step following the cooking/pasteurizing cycle as it stops the cooking process, prevents over processing, and restricts bacterial growth. Once the product has been heated to the proper internal temperature, and for the required time period, it is important to minimize any opportunity for the growth of micro-organisms in the +120.degree. F. to +60.degree. F. range. Thus, quick cooling of the product down to refrigeration temperature of 35.degree.-40.degree. F. results in restriction of microbial growth and prevents autolytic changes in the product.
Other methods of processing usually require moving the product from one container to another such as from an oven to a cold box. However, in that prior art method the recording of both time and temperature cannot be continuously maintained.
4. Objects of the Invention
It is the object of this invention to automatically cook food in packages, using heated water, so as to reach the pasteurization temperature at the core of the food without overheating or overcooking.
It is a further object of this invention to provide a water heated cook tank which maintains a uniform temperature in the tank within 0.2.degree. C.
It is a further object of this invention to start the cooling sequence immediately following the cooking/pasteurizing cycle as the cooling stops the cooking process, prevents overprocessing, and restricts bacterial growth.
It is a further object of this invention to cook and rapidly cool the cooked product while the food product remains in the same container.
It is a further object of this invention to maintain a complete and unbroken record through the thermal heating and cooling process of both the time and temperature so as to insure that complete cooking has taken place and the cooking cycle has been successful.
It is a further object of this invention to process various sizes of vacuumized and sealed pouches containing food product servings from several ounces to about 8.5 to 10 pounds.
It is a further object of this invention to utilize only "3A-dairy" type sanitary fittings and components allowing quick and manual disassembly for cleaning without requiring tools.
It is a further object of this invention to provide a pouch/package transport and holding system which protects and isolates each pouch or package while allowing full exposure of each to the process water.
It is a further object of this invention to use custom made thermocouple probes and a self sealing membrane as a means of monitoring the food core temperature.
It is a further object of this invention to provide a micro-processor to control all of the mechanical and electrical functions required in the thermal processes.
It is a further object of this invention to provide a temperature and time control utilizing a software program (F-Valve) which determines a predictable means of bacterial destruction.
It is a further object of this invention to use an integrated food thermal processing apparatus and method which retains the organoleptic properties of the food and extends the refrigerated shelf life of the food.
These and further objects of the invention will become apparent as the description of the invention proceeds.